Although Cable Television (CATV) networks originally delivered content to subscribers over large distances using an exclusively RF transmission system, modern CATV transmission systems have replaced much of the RF transmission path with a more effective optical network, creating a hybrid transmission system where cable content originates and terminates as RF signals over coaxial cables, but is converted to optical signals for transmission over the bulk of the intervening distance between the content provider and the subscriber. Specifically, CATV networks include a head end at the content provider for receiving RF signals representing many channels of content. The head end receives the respective RF content signals, multiplexes them using an RF combining network, converts the combined RF signal to an optical signal (typically by using the RF signal to modulate a laser) and outputs the optical signal to a fiber-optic network that communicates the signal to one or more nodes, each proximate a group of subscribers. The node then reverses the conversion process by de-multiplexing the received optical signal and converting it back to an RF signal so that it can be received by viewers.
Cable television (CATV) networks have continuously evolved since first being deployed as relatively simple systems that delivered video channels one-way from a content provider. Early systems included transmitters that assigned a number of CATV channels to separate frequency bands, each of approximately 6 MHz. Subsequent advancements permitted limited return communication from the subscribers back to the content provider through a dedicated, small low-frequency signal propagated onto the coaxial network. Modern CATV networks, however, provide for not only a much greater number of channels of content, but also provide data services (such as Internet access) that require much greater bandwidth to be assigned for both forward and return paths. In the specification, the drawings, and the claims, the terms “forward path” and “downstream” may be interchangeably used to refer to a path from a head end to a node, a node to an end-user, or a head end to an end user. Conversely, the terms “return path”, “reverse path” and “upstream” may be interchangeably used to refer to a path from an end user to a node, a node to a head end, or an end user to a head end.
Recent improvements in CATV architectures that provide further improvements in delivery of content include Fiber-to-the Premises (FTTP) architectures that replace the coaxial network between a node and a subscriber's home with a fiber-optic network with RF modulated optical signals. Such architectures are also called Radio Frequency over Glass (RFoG) architectures. A key benefit of RFoG is that it provides for faster connection speeds and more bandwidth than current coaxial transmission paths are capable of delivering. For example, a single copper coaxial pair conductor can carry six phone calls, while a single fiber pair can carry more than 2.5 million phone calls simultaneously. FTTP also allows consumers to bundle their communications services to receive telephone, video, audio, television, any other digital data products or services simultaneously.
Hybrid Fiber Coax (HFC) is commonly used for residential broadband data service delivery. HFC typically includes a coaxial cable connection in the last mile between the content delivery network and the customer premises. Passive Optical Networks with binary modulated instead of RF modulated optical signals are deployed to provide FTTP solutions. Even though PON networks send approximately 1 Gbps of data per service group in both directions, a typical PON architecture ‘overlays’ an HFC-modulation-type video wavelength to achieve larger downstream capacities. HFC is perceived as less capable than PON in the context of a total capacity for delivery of content, particularly in the upstream. Other “last mile access” technology that has limited upstream capabilities include a) legacy telephony twisted-wire infrastructure, exploited via DSL, ADSL and VADSL b) Wireless, of various kinds: Satelite for video and data, WiFi for data, LTE for data, voice, video and c) Fiber to the premises (FTTP), which has been successful for ‘point to point’ configurations, or for point-to-multipoint (P2MP) ‘passive optical network’ (PON) configurations for data, video and voice.
In an RFoG environment, where many of the physical limitations of the HFC cable plant do not exist, DOCSIS 3.1 could achieve significantly more capacity. A well thought out partnership of DOCSIS 3.1 and RFoG can satisfy the anticipated growth in traffic demand while providing MSOs with plant and equipment investment protection well into the future. Modifications to a traditional RFoG architecture may be introduced such that the attainable capacity is significantly more than anticipated for RF modulated signals and surpasses that of most binary modulated PON solutions.
Thus, improvements in the RFoG environment to increase capacity are desirable.
It is noted that while the accompanying Figures serve to illustrate embodiments of concepts that include the claimed invention, and explain various principles and advantages of those embodiments, the concepts displayed are not necessary to understand the embodiments of the present invention, as the details depicted in the Figures would be readily apparent to those of ordinary skill in the art having the benefit of the description herein.